Aquatic toxicity assessment of two abandoned mine sites in the Lake City Mineral District, Colorado

In preparation for reclamation, an assessment was made in June 2002 of two mine sites in the Lake City Mineral District, Colorado. Use was made of the recently developed Mine Waste Decision Tree for assessing aquatic toxicity. The Chicago Tunnel site (off Schafer Gulch, which drains into Henson Creek) is an actively draining adit whose water is a pH of 6.5. The Golden Wonder Complex (which can drain into the Gunnison River just below Lake San Cristobel) consists of two adits that had only a trickle of water flowing from them whose pH was between 4.5 and 5.5. Two features of the decision tree were especially useful: when the paste pH of the mine waste pile is less than 5, then water flowing from that pile can be considered to be toxic to the aquatic environment; and the leachate tests used in the decision tree provide a good indication of the element concentration pattern that would be found in water flowing from the waste pile. The assessment found that the Chicago Tunnel water and waste pile represented little threat to the environment. However, the Water flowing from the Golden Wonder Complex would be quite toxic if it ever reached the Gunnison River.